I'm not entirely sure I see the value proposition for C++ here. We already have e.g. std::array and std::vector, and AFAICT the other bits of this could be impl

I'm not entirely sure I see the value proposition for C++ here. We already have e.g. std::array and std::vector, and AFAICT the other bits of this could be implemented as templates? (Granted, std::array and std::vector don't require bounds checking unless you use at(), but there's nothing that says you couldn't implement two other template classes exactly like them which mandate bounds checking. std::array and std::vector usually do bounds checking in debug mode, but I'll grant that debug mode may be too slow.)